1. Field of the Invention
The present invention relates to a liquid crystal driver circuit which may apply to a liquid crystal display unit.
2. Description of the Related Art
The inventors of the present application know of a liquid crystal driver circuit which is arranged as an 8-level gradation digital system which operates so that one of eight reference voltages may be selected by an analog switch in accordance with three pieces of data fed from the outside of the circuit and the selected reference voltage may then be output.
A recent trend exists wherein liquid crystal display devices are being made larger and larger in size. The liquid crystal driver circuit is requested to suppress an output impedance accordingly. The known circuit is, as mentioned above, arranged so that its output impedance is defined by the analog switch. In order to lower its output impedance, hence, the larger transistor is employed for composing the analog switch.
With the foregoing method for towering the output impedance, however, as the transistor becomes larger, the overall circuit chip is increased in size. In particular, a large liquid crystal display unit needs a lot of Liquid crystal driver circuits. If the necessary driver circuits using larger transistors are integrated on one chip, the overall circuit chip size is made much larger. This presents a large obstacle to lowering the cost and the reducing power consumption.